Wired: Students 3D-Print Their Own UAS

Wired: Students 3D-Print Their Own UAS

It was supposed to be a big moment for the two brothers — both University of Virginia engineering students — the culmination of months of designing and refining. On a sunny day last August, Steven Easter and Jonathan Turman stood in the middle of a verdant field at the Milton Airfield in Charlottesville, VA, and watched anxiously as their 6.5-foot-wingspan drone aircraft taxied toward takeoff position.

Twenty or so government executives and advisers were watching. Cameras were rolling. Then, after just a few feet of taxiing, the unthinkable happened. The plane’s landing gear snapped off like a twig.

“The grass was pushing the landing gear back and forth, forward and back, not just up and down,” says Easter. “And it broke off pretty quickly — somewhat embarrassing. That was it for the day. Game over.”

Normally, that would have been a major setback. But this plane had one advantage over the standard SIG Kadet Senior model aircraft it was modeled after. The entire plane — from the nose to the rudders — had been designed in software and printed in lightweight plastic on a Stratasys 3D printer. Instead of a balsa-wood frame, the brothers printed a plastic exoskeleton that clipped together using connectors of their own design. Each of the plane’s components could pop on or off for rapid deployment, repair or, in this case, a quick redesign.

Professor Sheffler, with brothers/lab partners Steven Easter and Jonathan Turman, shows off the exoframe of “Wendy,” their 3D-printed plane. Photo: University of Virginia

The brothers zipped back to their workshop to make a lesson of the broken landing gear. “We didn’t have to go and make a new plane, we just pulled off the one piece that was broken and did a couple days of redesign, reprinted it, and by the next week we were ready to go,” says Turman.

And on the subsequent attempts, the plane flew beautifully.

The “Wendy” aircraft — named for Turman and Easter’s mother — is the latest demonstration of the power of 3D prototyping. The project is the brainchild of Michael Balazs and Jonathan Rotner, two scientists at research and engineering firm MITRE’s Center for Integrated Intelligence Systems. Their mission, jointly funded by the Department of Defense and MITRE, is to develop cheaper and faster solutions to expensive government programs, such as building autonomous aircraft.

“[We're] trying to achieve 90 percent capabilities of what the big companies can do, but at 10 percent of the cost,” Balazs says. “So we leverage everything from open technologies to commercial off-the-shelf systems to agile advanced manufacturing, to show the government that they can meet their robotics goals of unmanned systems, whether they’re ground, aerial, underwater or whatever it is.”

Wendy is their best example so far. In addition to its 3D-printed body, it uses a common Android smartphone as the sophisticated on-board brain of the aircraft’s system.

Autonomous model planes and helicopters are commonplace now — everything from handheld units to full-sized warplanes. Many of the smaller systems use off-the-shelf model aircraft, like the Kadet Senior, and add specialized on-board autopilot circuitry to the plane’s standard radio controls so the aircraft can fly itself through a variety of patterns or programs.

These autopilot systems are still expensive, running into the $10,000 range for high-end units with the level of reliability needed by MITRE. Moreover, the planes aren’t truly autonomous. Much of the computation is performed by a dedicated ground station — another $20,000 — that communicates with the on-board autopilot computer over Wi-Fi.

For the MITRE scientists, that was unacceptable. Last fall, as an extension of their ground-based Android robotics research (which employs, in part, eight university interns), Balazs and Rotner decided to set up an airborne program to test the use of low-cost, readily available smartphones for piloting. They started with a Galaxy Nexus, programming it as an on-board replacement for the ground station. The phone would access the autopilot’s telemetry data, process it and, based on location and heading, send or change the waypoints the autopilot would be following.

The first step was to crack the Nexus’ security — they had to root the phone to make it run in ad hoc Wi-Fi mode, rather than infrastructure, so it could talk directly to the autopilot without an access point to act as an intermediary.

Once development was under way on the control system, the scientists decided they needed a faster and easier way to get their platform airborne — common RC plane kits can take many weeks or even months to assemble, and they needed something that could be useable with a few days’ notice.

“That’s where we came up with the idea for the 3D-printed plane,” Balazs says. At the start of February, they began searching online for ideas, and found an example of a basic printed model plane from the University of Southampton in the UK. But the also noticed something interesting much closer to home.

A few miles away at the University of Virginia, aerospace engineering professor David Sheffler had just completed a new, unique course where students spent an entire semester designing and building a 1/4 scale replica of the Rolls-Royce AE3007 jet engine. To keep costs manageable (an actual AE3007 costs about $2 million), Sheffler had the students print their components in the school’s new, state-of-the-art 3D-printing lab, using high-end Stratasys machines, and assemble the pieces around bearings and a propshaft he had milled specially for the project.

On their first try, the engine worked well. “We hooked it up to the compressor and got it to spin up to about 2,000 RPM. It was a big success,” Sheffler explains. “I had a student filming it on his iPhone, and the next day he plopped it on YouTube.”

That YouTube video caught the eye of the MITRE team as they researched the viability of a 3D-printed aerial platform. Balazs and Rotner realized they might have found the right person to lead the build of their aircraft.

“The government doesn’t really have interest in small model turbine engines, but they might have an interest in being able to print a robotic platform,” Balazs says. “So we met with professor Sheffler and said, ‘Hey, would you be interested and do you think we could do this?’”

He said yes to both questions.

Sheffler e-mailed a cryptic note to the engineering students: he was looking for two summer interns for a 3D-printing project. He received only one response, from Easter, who brought his lab partner and brother Turman along for the meeting. The duo was surprised to see six executives in suits as they walked into the room.

The brothers began working on the project in May, spending upwards to 80 hours per week in the lab creating and refining their design. One of the first and biggest obstacles they encountered was the heavier weight and greater deflection of printed plastic over the balsa wood typically used to build the plane they modeled their design on. This meant that, rather than just printing the same pieces in a kit, they’d have to completely re-engineer the frame’s design.

Fortunately, they could print the plastic to take any shape they could design on their CAD system, allowing them to create designs that would be impossible to make solely out of wood. That also allowed them to make on-the-spot modifications; at one point, as the printer laid down layer after layer of plastic, the MITRE scientists called the brothers with a big design change. The plane needed ailerons to work correctly with the autopilot being used. Hardly skipping a beat, the brothers modified the files to incorporate that element, and let the printer add it to the existing printouts.

They also took advantage of the printed aspect to design and incorporate rapidly deployable, Lego-like connectors for each of the plane’s components. Different types of connections were devised, printed, and tested as the pieces started to take shape.

Finally, in August, they set up for the maiden flight — which proved disastrous. But their subsequent attempts were hugely successful. The printed platform and its Android brain both handled everything asked of them.

“Our pilot informed us it was very easy to fly and didn’t need a lot of hand-holding,” Easter says. “It had a lot of lift naturally and could glide a long ways. The first landing was a slightly rough, as the pilot was adjusting to the flight characteristics, but the second landing — we flew twice that day just to be sure — was very graceful.”

So how will this type of system be used? “You’d love to be able to set up four or five of these things to fly above a forest fire,” Balazs says. “You’d use the camera right there on the phone to snap pictures. They’re all geolocated using the GPS on the phone. You’d put a temperature sensor on there … Where you find the hottest part of the fire and the strongest wind, that’s the area where you need to fight the fire.”

“Even an inexpensive government or traditional system is going to cost you at least $150,000, but more likely closer to a quarter of a million or more, to have an aircraft that will go up and do that,” he continues. “So you can imagine, you put a printer out there in Colorado, they print out the number they need, they grab a bunch of phones from the local store, some servos, they can throw it together in a couple days, have these things flying over the forest fire, collaborating on the sharing of data, ones reading wind data a little bit north saying ‘In a few hours your wind is going to be like this…’”

Rotner continues, “We are trying to present it so it is immediately and cheaply impactful to local fire depts, FEMA, border patrol, DHS, as well as DOD. It’s not just military usable.”

Indeed, one of the big successes with the maiden flights were aerial maps. On the plane, the phone was placed underneath with the camera facing downwards. The Lapse It Pro app snapped a photo every few seconds.

After landing, another program quickly processes those images into a mosaic of everything the plane saw while it flew. It took about five minutes.

Of course, in these times, drones are more commonly associated with less benevolent applications — U.S. military air strikes that have killed terrorists and insurgents in countries like Pakistan and Yemen, at the cost of possibly hundreds of civilian lives. Balazs and Rotner’s excitement is tempered slightly when asked about the possibility of their autonomous plane being used for hostile purposes — a real-life version of Real Genius.

“The work we do is for data collection — we’re not on the offensive side,” Balazs says, explaining, hopefully, that the physics of the platform make that less feasible. “It is the SWaP [size, weight and power] of such systems that are prohibitive,” he states, noting that their platform offers no offensive capabilities that couldn’t have be done by someone with an RC aircraft and malicious intent.

When completed, MITRE’s system will offer a drastic price reduction over the expensive custom UAVs that are contracted by the government. The initial printouts of the frame cost $5,500 to produce and refine — a price that will go down even further once the design is finalized and optimized, and as the cost of printing lowers. Motor, servos and components for the plane were around $1,500. And once the they remove the dedicated autopilot unit and set it to run entirely by Android control — their next milestone — the only other material cost will be a few hundred bucks for a smartphone.

Hitting their fully-Android goal has a purpose: by 2015, there’s an expectation that UAV drones will be permitted to fly in the national airspace. MITRE is help to determine the policies for this, and Balazs states that the FAA’s requirements may make it difficult for hobbyist autopilot units to receive full clearance. One reason is the FAA’s demand that the circuitry will have intelligent crash landing capabilities, so drones, as Rotner puts it, “don’t crash into a highway.”

They believe the Android platform will be suitable for these requirements. “You’re going a system that can see where it is and determine a soft area to direct itself to,” Balazs explains. “The hobbyist systems are fantastic but they’re never going to move into the non-hobbyist FAA requirements. We’re trying to make our system work with this. The phone can very easily determine the road instead of a green patch on the road.”

Testing for this next iteration is already being planned. With the success of the initial craft, MITRE has approved two follow-on contracts for continuing research and development, the first of which will allow the all-Android system to go airborne sometime this spring. That contract will also have the brothers redesigning the current aircraft to make structural and performance improvements, including reducing weight and adding wing-mounted cameras.

The second contract is for a smaller version of the first plane that comprises two or three modular pieces instead of the 17 parts of the original design, making it much easier to handle. The current plane has to be shipped in a 2′x2′x8′ crate, even though it is able to be snapped apart, due to having a tightly applied plastic skin that increases its aerodynamics. The new, smaller design will allow for more rapid deployment, including an easier ability to ship the plane via UPS. And while the funding of the original plane means its design files likely will remain closed, Balazs says the team is “looking to take a more open approach” to the second, meaning they may be able to release the CAD files for others to modify and improve on themselves.

The creation of a full plane takes about three weeks from start to finish. “The time from redesign of concept to redesign in CAD to printing is so much smaller than it used to be” Rotner explains. But most of that timeframe comes from to technological limitations.

“The real bottleneck at this point is simply the speed that the printers can print out,” Balazs continues.”But five to ten years, it’s going to be a non-issue. We’ll see increases in speed and materials in the next couple years.”

When he thinks about the long-term potential of the technology, his mind turns to NASA’s 1970 Apollo 13 mission, during which Earth-bound engineers were given a matching set of the spare parts available to the astronauts to determine how to build a solution for filtering CO2 after an on-board explosion.

“With all of these systems, the Android system and the 3D-printing system, we want to go beyond that. We want to give them a printer out wherever they are and say, ‘Here, we’ll just print out what you need and solve your problem.’”